Crossed-field tube coupling apparatus



y 1965 A. s. WILCZEK ETAL 3,185,885

CROSSED-FIELD TUBE COUPLING APPARATUS Filed Aug. 1, 1962 FIG] o of 3. e w ww w nfvwowv INVENTORS RICHARD F. DOYLE ANDREW S. WILCZEK ATTORNEY United States Patent 3,185,885 CROSSED-FIELD TUBE (ZUUPLING APPARATUS Andrew S. Wilczelr, Sid Bridge, and Richard F. Doyle, Maplewood, NJ., assignors to fi-iF-D Laboratories, inc, Union, NJ, a corporation of New Jersey Filed Aug. 1, 1962, Ser. No. 214,115 6 Claims. (Cl. 315-35) The present invention relates in general to microwave devices of the type wherein a traveling electromagnetic wave of phase velocity less than the velocity of light interacts with a stream of particles (for example, electrons) and more particularly to coupling structures for coupling wave energy to or from the slow-wave circuits utilized in crossed-field devices such as crossed-field amplifiers and magnetrons.

Crossed-field devices are presently being built utilizing slow-wave structures made up of an array of resonant elements wherein the resonant elements are conductors which extend for a distance (Mug (A =wavelength reference operating frequency, 11:0, 1, 2, etc.) between two spaced-apart short circuiting planes. Slow-wave circuits employing an array of such elements are characterized by high interaction impedance and high power handling capabilities.

With such slow-Wave structures described above diiiiculty has arisen in providing means .for conveniently coupling energy to and from the slow-wave circuit. Typical prior art structures have been rectangular waveguides or coaxial lines connected to a portion of the circuit and extending radially outwardly from the envelope thereof.

The arrangement of input and output coupling means projecting radially outwardly from the tube envelope produces certain disadvantages in construction of the tube such as the fabrication, the mounting of parts, the assembly of the tube, and the mounting and replacement of the tube in its focusing structure. The vacuum envelope must be broken in its broad sides. In many cases the input and output couplings can only be connected to the circuit after the circuit has been mounted inside the tube envelope. The focusing structure must be broken to permit passage of the input and output therethrough, and in many cases the focusing structure has to be removed from its mounting when a tube has to be repaired or replaced. This latter difiiculty prevents the use of such tubes in phased arrays.

Also, a waveguide tapered outwardly from the tube to a rectangular waveguide large enough to propagate microwave frequencies in the operable range of the type of tube described herein is often much, much larger than the other parts of the tube, thereby making the use of rectangular waveguide input and output coupling means extremely undesirable.

The present invention relates to slow-wave circuits utilizing an array of resonant conducting rods for a slowwave structure and provided with coaxial lines with the mes thereof parallel to the ax s of the conducting rods for coupling energy to and from the slow-wave structure.

Advantageously, the axes of the coaxial lines are parallel Another feature of the present invention is the provision of a Wave propagating structure including an array of conducting elements, coaxial line means with the axis thereof parallel to the axes of the elements of said array for coupling energy to or from said array, a pin connecting the center conductor of the coaxial line means to the closest of said conducting elements, and a quarter-wave stub for supporting the center conductor of the coaxial line means.

Another feature of the present invention is the provision of a conducting element array, wave propagating structure for a circular crossed-field device wherein coaxial input and output lines are connected to the conducting element array with the axes of said coaxial lines parallcl to the axis of the device.

These and other features and advantages of the present invention will become more apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein,

FIG. 1 is aside cross sectional view of a circular crossediield amplifier embodying the present invention,

FIG. 2 is a fragmentary cross sectional View of a portion of the structure shown in FIG. 1 taken along line 22 in the direction of the arrows, and

FIG. 3 is a cross sectional view showing a portion of the structure of FIG. 1 taken along line 33 in the direction of the arrows.

Referring now to the drawing illustrating a crossed field amplifier utilizing the present invention the tube comprises an evacuated envelope 11 provided with a cathode electrode assembly 12 coaxially located therein and an anode electrode assembly 13 surrounding and spaced from the cathode assembly 12 to define a wave-electron stream interaction region 14 therebetween.

The cathode electrode assembly 12 includes a continuous cylindrical cold cathode 15 made of a material having a secondary emission ratio such as beryllium-copper, which is supported coaxially within the tube by means of a shaft 16 of, for example, copper extending through the lower of a pair of annular header members it? which are made of a magnetic material as, for example, iron, to serve as pole pieces. The shaft 16 serves as the cathode connection for the tube and is electrically insulated from the remainder of the tube by means of an annular insulator 19 of, for example, glass. The cathode is provided with a pair of end hats 21 of, for example, iron which confine the emitted electrons to the interaction region 14 between the cathode assembly 12 and the anode assembly l3.

The anode assembly 13 includes an array of half-wave resonant conducting rods or elements 22 of, for example, molybdenum which are distributed along spaced-apart top and bottom shorting members 23 and 24, respectively, of, for example, copper to form a slow-wave structure. The standing wave pattern established on such resonant elements exhibits characteristic regions of high electric field intensity, referred to herein as capacitive regions, and characteristic regions of high magnetic field intensity, referred to herein as inductive regions. In the structure of FIGS. 1-3 a capacitive region C exists near the center of the conducting rods 22 and an inductive region L exists near the shorted ends of each rod (see FIG. 1).

in order to increase the interaction bandwidth of the slow-wave structure and insure forward wave interaction each conducting rod 22 is provided in the central capacitive region thereof with a conducting member 25 of, for example, copper with extending portions 25 of, for example, copper disposed in spaced-apart relationship with respect to the extending portions 26 of conducting members 25 on the two alternate conducting rods 22 closest thereto to form capacitive coupling gaps 27 therebetween in the manner as taught and claimed in copending application U.S. 164,008, filed January 3, 1962, titled Slow Wave Circuit, inventor Hunter L. McDowell, and assigned to the same assignee as the present invention. One band ofconducting membersZS couples or electrically straps together one set of alternate conducting rods 22, and a second band couples or electrically straps the remaining rods 22.

The slow-Wave structure is interrupted to provide a drift segment 28. On opposite sides of'the drift segment 28 input and output coaxial lines 31 and 32 respectively, are mounted on shorting members 23 and 24 with the axes of coaxial lines 31 and 32 parallel to the axes of the conducting rods 22 of the anode assembly 13. According to the preferred embodiment shown the coaxial lines 31 and 32 project out of opposite ends of the envelope 11 and have their axes parallel with the tube axis. Under certain circumstances it may be desirable 4 voltage applied between the grounded anode assembly and the cathode shaft 16.

In operation, a signal which it is desired to amplify is fed to the slow-wave circuit of the anode electrode assembly 13 via the input. coaxial line 31. This signal establishes a traveling-Wave in the interactionregion 14 of sufiicient intensity to initiate the emission of electrons from the cold cathode 15, and by secondary emission due to back bombarding electrons which have gained energy from the wave. This emission can'be sustained without the necessity of supplying external heating power.

The interacting electron stream moves through the A region 14- with a clockwise circumferential velocity dcto have both coaxial lines 31 and 32 project out of the 7 same end of the electron tube.

Each of the coaxial lines 31 and 32 has an outer conductor 33 of, for example, copper, and a center conductor 34 of, for example, molybdenum and is provided with a vacuum tight wave permeable window 35 of, for example, alumina ceramic sealed between the outer and center conductors 33 and 34, respectively. A conducting pin 36 of, for example, molybdenum connects the closest conducting rod 22 to the center conductors 34 of input and output coaxial lines 31 and 32 to couple the coaxial lines 31 and 32 to the remainder of the slow-wave circuit. The impedance of the coaxial lines 31 and 32 is matched to that of the slow-wave structure by locating the pin 36 the proper distance from the shorting members 23 and 24. A maximum resistive component of impedance is seen from the pin 36 looking toward the rod 22 when the pin 36 is located at the rod 22 center. This impedance varies smoothly to zero at the end of the rod 22;

The outer conductors 33 of the input and output coaxial lines 31 and 32 serve as the first and last conducting is provided with an axial hole for supporting the center conductor 34. The quarter-wavestub 37 provides 'a rigid support for the center conductor 34 while looking electrically like an open circuit. a

By the input and output coupling construction described above the input and'ou'tput signals are applied and taken from the slow structure in the smallest space possible and the input and output 'connections to the tube are positioned parallel to the axis of the tube. In this manner, the tube can beam'ally inserted into its focusing structure, described below. 'Thus, a tube of this construction is especially useful in phased arrays since the tube can be removed from its focusing structure for repair or replacement without disturbing the focusing struc ture.

While it is desirable to have theouter conductors 33 of the coaxial lines 31 and 32 the same size as the conducting rods 22 of the slow-wave structure, this is not absolutely necessary. However, if the outerconductors 33 are the same diameter as the conducting rods 22 the tube is more easily designed and matched electrically.

The tube is evacuated and sealed by means of a pincha off tube 41. I a

aligned with and surrounding the tube. Thecrossed elec tric field in the region 14 is provided by means of a negative termined by the ratio of electric-to-magnetic field. The phase velocity of the traveling-wave is approximately synchronous with this electron stream velocity for a wide band of frequency so that the electrons deliver energy to and amplify waves within this band, the amplified output signal being taken out through the output coaxial line 32. The drift segment 28 is'of suflicient length to permit electron debunching so that electrons may reenter the interaction region for improved efiiciency without producing undesired internal feedback. However, debunching is not necessary so that the drift space can be just a very short space which is possible with the present invention since the input and output couplings according to the present invention are positioned within a rod of the slow-wave structure.

A circular crossed-field amplifier tube constructed according to the present invention for a frequency range of from 1150 to 1300 megacycles and which produces a peak output power on the order of kilowatts with a gain of 20 db is less than 15 inches long and 4 inches in diameter.

While'the invention has been described with respect to circular crossed-field amplifiers it is adaptable for the output of a magnetron oscillator. In a magnetron since the coaxial line would only be weakly coupled to the 'slow wave circuit instead of matched the pins 36 would be connected closer to the shorting members 23 and 24 than in an amplifier. Also itis useful in planar type tubes which utilize a slow-wave structure of the type described above, but such tubes will not have the advantage of having the axes of the input and output coaxial lines parallel to the tube axis. For example, the invention can be used in so-called M-type tubes and O-type tubes but since the conducting rods of the resonant circuit will probably not beparallel to the axis of the tube neither will'the axes of the input and output coaxial lines.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. What is claimed is:

1. A Wave propagating structure comprising (a) an array of resonant conducting rods distributed along desired path of Wave propagation, (b) at least one of said rods being hollow, and extending along its axis away from said array, (0) a center conductor positioned within said hollow 7 rod, and (d) means for coupling said center conductor to an adjacent rod, said' center conductor and said hollow Iod comprising a coaxial line for coupling wave energy to or from said slow-wave structure.

2. The wave propagating structure according to claim 1 including means formin g a shorting member in one "end of said hollow conducting rod contacting and rig-idly supporting said center conductor.

3. A microwave electron tube apparatus including; means forming a cathode electrode structure for supplying a stream of electrons; means forming a slow wave circuit disposed adjacent said stream of electrons for electron interaction therewith; means for extracting wave energy from said slow wave circuit for propagation to a suitable load; said slow wave circuit including, an array of substantially parallel directed elongated conductive bars; means for electrically strapping said bars to form a slow wave propagating circuit; said means for extracting wave energy from said circuit including, a hollow bar substantially parallel directed to said first array of conducting bars and disposed adjacent said array and axially coextensive with a substantial portion of said array, said hollow bar including a center conductor therein thereby forming a coaxial transmission line, and said bar having an aperture in the wall thereof with an extension of the center conductor passing therethrough and coupled to one of the conductive bars of said array of bars for coupling wave energy therebetween.

4. The apparatus according to claim 3 wherein said cathode electrode structure is cylindrical and includes an arcuate electron emissive portion, said array of conducting bars being arcuate and coaxially disposed of said cathode electrode structure and at least partially surrounding same, and the tube apparatus including means for producing an axial magnetic vfield permeating the electron stream for producing a magnetron type inter action.

5. The apparatus according to claim 4 including means apertured with an extension of said center conductor passing through said aperture and being coupled to an adjacent bar of said slow Wave circuit for coupling wave energy therebetween.

6. The apparatus according to claim 3 wherein said hollow conductive bar for extracting signal wave energy includes, a shorting conductive member closing off one end of said hollow bar to form a short therein, said shorting member being disposed approximately a quarter wave length at the center operating frequency of said slow wave circuit from said extension of said center conductor which passes through said aperture in said hollow bar.

References Cited by the Examiner UNITED STATES PATENTS 2,907,913 10/59 Dench 3153.5 2,928,986 3/60 Wilbur 3l539.53 X

GEORGE N. WESTBY, Primary Examiner. 

1. A WAVE PROPAGATING STRUCTURE COMPRISING (A) AN ARRAY OF RESONANT CONDUCTING RODS DISTRIBUTED ALONG DESIRED PATH OF WAVE PROPAGATION, (B) AT LEAST ONE OF SAID RODS BEING HOLLOW, AND EXTENDING ALONG ITS AXIS AWAY FROM SAID ARRAY, (C) A CENTER CONDUCTOR POSITIONED WITHIN SAID HOLLOW ROD, AND (D) MEANS FOR COUPLING SAID CENTER CONDUCTOR TO AN ADJACENT ROD, SAID CENTER CONDUCTOR AND SAID HOLLOW ROD COMPRISING A COAXIAL LINE FOR COUPLING WAVE ENERGY TO OR FROM SAID SLOW-WAVE STRUCTURE. 